Before purchasing a VoIP system, enterprises need to carry out careful research as VoIP vendors offer intricate products with varying capabilities.

Today's IP PBX market offers a range of services that should satisfy almost any business requirement. But selecting the right IP PBX for your business can be a complicated process, mainly because of the various IP PBXs, features and services offered.

You should consider four major criteria when purchasing an IP PBX product: VoIP features and functions, an end-to-end service vendor, redundancy capabilities, and expanding user and device support. Let's take a look at some leading VoIP vendors and examine how their products fit into these categories.

Important VoIP features and functions

SIP trunking is a feature that should be present on any IP PBX today. Some vendor models, such as the Mitel 3300 series, can support up to 2,200 SIP trunks. NEC's Univerge can support up to 4,000 SIP trunks, while Cisco's CUCM can exceed these figures with the appropriate VoIP infrastructure.

Toshiba's IPedge can support up to 440 SIP trunks. Panasonic's KX-TDE supports up to 64 SIP trunks. ShoreTel and Adtran do not specify their maximum support for SIP trunks, but I'm sure they would be able to support an SMB.

Businesses with call-center services might want to consider systems with a high number of SIP trunks, as they usually require connections to multiple providers, both local and international.

Do early research on IP phones

Phone design and functionality play a critical role in the buying decision. VoIP vendors such as NEC, Panasonic, Mitel and Toshiba let customers select IP phones or digital phones. This is a major advantage, especially for businesses upgrading from a PBX to an IP PBX, as it might be possible to re-use their existing digital or analog phones with the new IP PBX.

On the other hand, vendors such as Cisco, Adtran and ShoreTel offer only IP phones as part of their portfolio, though customers can also connect analog phones to the IP PBX using analog telephone adapters (ATAs).

In terms of variety, Cisco and Mitel are the only two vendors that offer more than 25 different IP phone models -- from simple single-line IP phones to multi-touch color LCDs. Cisco's top IP phone models also offer video capabilities.

NEC's UT880 IP phones are also impressive, offering full unified communications (UC) functionality geared for executive users. ShoreTel offers more than 15 IP phone models with similar functionality as other vendors.

Because of the large variety of IP phones, businesses need to examine the phones offered by each vendor before proceeding with the purchase of their IP PBX. Also note that some IP phone models are only compatible with the IP PBX service from the same vendor. So, if you want to mix and match different vendors, ensure the phones are compatible with the service.

Some warnings about remote user support

User mobility is a growing trend and supported by all vendors, but some caveats need to be examined. All VoIP vendors offer a proprietary mobile application that is available for the Windows platform -- for mobile laptop users -- and iPhone and Android users. Yet, in almost all cases, this setup requires a virtual private network (VPN) so remote users can connect to their headquarters before logging on to the IP PBX system.

ShoreTel provides mobility support via its dedicated mobility router appliances, though it requires purchasing additional hardware and licenses. Cisco can integrate VPN support on its voice gateway, which requires an additional security license and offers a mobile VPN-less option based on its Expressway servers -- all part of the Business Edition platform. The VPN-less approach requires additional licensing and hardware infrastructure in the form of a firewall and router.

Mitel's 3300 CXi II controller offers a wide area network (WAN) port for direct Internet connectivity, supporting network address translation (NAT) and firewall services, but lacks the ability to support VPN. Adtran does not offer support for Internet connectivity, firewall and VPN services with its NetVanta 7060 platform.

Voicemail port support

Voicemail is considered a standard feature of any IP PBX. While all systems support voicemail features, you should ensure your system can support enough mailboxes to meet your organization's needs. You should also ensure it offers enough voicemail ports, which identify how many simultaneous users can log into the system and listen to their messages.

NEC's SV8100 supports more than 500 mailboxes but offers only up to 16 maximum voicemail ports -- NEC calls them voice response channels. Mitel's 3300 CX II can support up to 750 mailboxes and 16 voicemail ports. Some vendors do not clearly state how many voicemail ports their systems support.

VoIP vendors with and without end-to-end services

Only two vendors -- Cisco and Adtran -- currently provide an end-to-end solution.

Adtran is the only vendor that comes close to an end-to-end solution like Cisco. The NetVanta 7060 provides a built-in 24-port Layer-2 10/100 Gigabit Ethernet (GbE) PoE switch. However, it has no 1 GbE support and no support for Internet connectivity. In addition, the NetVanta line includes IP phones, Ethernet switches, routers and wireless access points.

Some VoIP vendors provide separate or built-in products worth noting, though these are not full end-to-end services. Mitel's 3300 CXi II controller integrates a 16-port Layer-2 10/100 GbE PoE switch and support for firewall and Internet connectivity. ShoreTel sells routers and VPN concentrator devices, but does not offer any network switches.

Redundancy combats network failures

Redundancy is an essential ingredient to any business that cannot afford downtime and runs mission-critical services via its communication infrastructure. IP PBXs that offer an all-in-one package seem to attract businesses because of their lower costs -- but they usually fail the redundancy test.

Communication failure does not necessarily occur only at the IP PBX level. WAN link failure is a common example, leaving remote sites without any telephony systems and intra-site communication.

Cisco's VoIP infrastructure allows multi-level redundancy at a higher cost. Cisco CallManager -- the main IP PBX product -- supports clustering, allowing multiple instances of CallManager to work together in a failover configuration.

Businesses need to examine the phones offered by each vendor before proceeding with the purchase of their IP PBX.

Cisco's voice gateways (ISR routers) connect the IP telephony infrastructure with telecommunication providers, but can also serve as a second backup device should the CallManager cluster fail. This is called survivable remote site telephony (SRST). When such a failure occurs, IP phones will automatically register to the voice gateway for basic phone functionality until the CallManager server or cluster is restored. During the failure of CallManager server or WAN link connecting the sites, remote site IP phones registered to the main office's CallManager servers will fall back to their local voice gateway, which will provide SRST services.

ShoreTel also offers products with redundancy capabilities. IP phones register with their local voice switch. When this voice switch fails, IP phones automatically register with a redundant voice switch that has been installed elsewhere in the network -- locally or at the headquarters. This transition happens automatically, minimizing downtime across the enterprise.

Mitel's 3300 controllers offer similar redundancy when deployed as part of the Mitel MiVoice Business service. Businesses can deploy a centralized IP PBX system similar to Cisco's CallManager while also providing SRST services to remote sites in the event of a WAN link failure.

The Toshiba IPedge EP server can be configured in a cluster mode, where each IPedge server is an individual node connected with the rest of the cluster, via the WAN or LAN. One server is configured as the primary node and centralized administration is performed via the primary node's Enterprise Manager. IP phones are configured to fall back to a secondary IPedge server when the primary fails.

Other VoIP vendors offer decentralized call processing, and therefore focus more on local system redundancy -- in case there is more than one IP PBX system installed. If redundancy is important to your business, be sure to identify which redundancy options you need.

Accommodating for business growth

Expanding your IP PBX system to support more users and devices as your business grows is important, as it helps curb costs and allows businesses to pay as they grow.

Mitel can support up to 999 controllers clustered together, so businesses simply add controllers and licenses to support the required amount of users. The milestone here for an additional hardware controller depends on your PBX model, starting with 150 users for the smallest Mitel Controller, the 3300 CX II.

NEC works along the same lines with its smallest IP PBX model -- the SV8100 -- supporting up to five IP PBX units stacked and around 90 to 100 phones per unit. The total number of phones supported per unit depends on the type of phones used.

Panasonic offers similar user expandability, but only with its KX-TDE600 model, which supports the base unit -- the main PBX -- plus up to three expansion shelves. Unlike other vendors, with Panasonic you simply purchase an expansion shelf and applicable licenses. The maximum number of phones supported by each expansion shelf depends on the type of phones.

ShoreTel supports user expansion by simply purchasing another voice switch, but does not specify how many voice switches can be added to a single site. I believe the number of voice switches depends on the model and business infrastructure.

Cisco's CallManager BE6000 can handle up to 1,200 devices with its medium-density servers, while Cisco's high-density servers push this limit to 2,500. To reach these limits, businesses must buy additional BE6000 servers, but the milestone for each server depends on the system's configuration and services offered. Licenses will also need to be purchased.

Toshiba offers a maximum of 128 IPedge servers in a network, allowing businesses to expand their user support to thousands. The exact figure depends on the overall system configuration, however the IPedge EP model offers support of up to 40 users per server, whereas the IPedge EM -- the largest available model -- supports up to 1,000 users per server. In addition to the hardware, additional user licenses will be required.

Find the service that fits your business

All of these products have pros and cons that you should compare with your organization's needs when purchasing an IP PBX system.

For large enterprises or expanding mid-size businesses looking at a complete IP PBX service with accompanying LAN infrastructure, the comprehensive services offered by Cisco, Toshiba and Mitel are probably your best bet. A small company with a basic LAN infrastructure that does not need VLAN segmentation and QoS might want a more hybrid service offered by Panasonic, NEC or Adtran.

Businesses must keep in mind that when moving to an IP-based PBX that involves IP phones, it is imperative their network infrastructure is VoIP-ready to ensure a smooth transition to the world of VoIP.

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